1. Field of the Invention
This invention relates to film feeding devices for cameras, and more particularly to film feeding devices of the type in which when exchanging a film cartridge, the rewind fork is axially moved to release the spool hub of the cartridge from the engagement with the rewind fork.
2. Description of the Prior Art
In cameras using 35mm film contained in cartridges, the means for permitting the cartridge to be put into and taken out of the cartridge chamber within the camera housing have forms which may be divided into the following two main classes.
One is of the type wherein the rewind fork of the camera is restrained from axial movement, and the size of the cartridge chamber is increased in the vertical direction (a direction parallel to the axis of the rewind fork), or the bottom wall of the cartridge chamber which is opposite to the rewind fork is provided with a cutout, whereby without creating an obstacle to the operation of bringing the key of the film spool of the cartridge (hereinafter described as "cartridge hub") into driven engagement by the rewind fork, loading and unloading of the cartridge is made possible. The other form which has been adopted by many up-to-date cameras is that the rewind fork is made axially movable so that with the rewind fork is retracted from the cartridge chamber, the operator can put in and take out the cartridge. According to this latter form, the size of the cartridge chamber can be minimized, and the degree of flexibility of the space in the vertical direction of the cartridge chamber can be improved in an advantageous manner due to a minimization of the bulk and size of the camera.
However, in such a camera, in order to exchange the exposed cartridge for a fresh one, the required steps include: axially moving the rewind fork to effect disengagement from the cartridge hub, removing the exposed cartridge from the chamber followed by putting in the fresh cartridge, and returning the rewind fork to the initial position for operative connection with the spool hub of the fresh film cartridge. Thus, the process for exchanging the cartridges can becomes troublesome. For this reason, according to the prior art, to simplify the exchanging operation, there has been proposed a device cooperating with the locking mechanism for locking the back cover of the camera in the closed position in such a manner that when the back cover is opened by releasing the locking mechanism, the rewind fork is disengaged from the cartridge hub, and when the back cover is closed, the rewind fork is automatically brought into engagement with the cartridge hub. Such a device can disclosed in U.S. Patent No. 3,096,699. Clearly, such a device can facilitate some of operations necessary to exchange the cartridges, and since the photographer needs to do little more than handling the cartridges, exchanging of the cartridges can be performed quickly and with ease. But, on the other hand, an alternate drawback arises in that a pull cannot be exerted on the film unless the back cover is closed. More specifically, with such a conventional device, when the back cover is in the open position, after the new cartridge has been placed in the empty chamber a difficult handling operation is encountered since the leader of the film must be pulled out of the cartridge far enough so the photographer can attach it to the camera side takeup spool. This is because the rewind fork is not in engagement with the cartridge hub when the cover is open and thus it is hardly possible to make sure the sprockets engage the film perforations.
Also in application to cameras of the so-called auto-loading type in which all the photographer needs to do to make the film ready to be advanced is to bring the film leader into engagement with the spool shaft of the camera side and then to close the back cover. It follows that, since the cartridge cannot be retained in the chamber until the back cover is closed, the removal of the operator's finger from the cartridge for example, just before the closure of the back cover often results in a backward turn of the cartridge by curling of the film. Therefore, there is the possibility that the film pullout slit in the cartridge casing will not be oriented towards the takeup spool when the back cover is closed. As a matter of course, under such condition, feeding of the film cannot be carried out, even though the rewind fork is engaged with the cartridge hub by closing the back cover. In addition, if the operator is not aware of such an accident, he will repeat fruitless camera actuations which do not expose new film.
Thus, conventional devices give rise to an additional problem in that when applied to the auto-loading type of cameras the reliability of the film feeding control cannot be improved.